Finite quasiparticle lifetime in disordered superconductors

Žemlička, Martin; Neilinger, P.; Trgala, M.; Rehák, M.; Manca, D.; Grajcar, M.; Szabó, P.; Samuely, P.; Gaži, Š.; Hübner, Uwe; Vinokur, V. M.; Il’ichev, E.

doi:10.1103/physrevb.92.224506

Cited by 26 publications

(22 citation statements)

References 29 publications

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“…This is not compatible with a pure BCS SDOS considering the thermal smearing at 450 mK. We address this phenomenon below but note that the complex conductivity derived from our recent experimental transmission measurements on coplanar waveguide resonators made of 10 nm MoC film shows a finite quasiparticle lifetime consistent with the existence in-gap quasiparticle states [26].…”

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confidence: 89%

Fermionic scenario for the destruction of superconductivity in ultrathin MoC films evidenced by STM measurements

et al. 2016

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We use sub-Kelvin scanning tunneling spectroscopy to investigate the suppression of superconductivity in homogeneously disordered ultrathin MoC films. We observe that the superconducting state remains spatially homogeneous even on the films of 3 nm thickness. The vortex imaging suggests the global phase coherence in our films. Upon decreasing thickness, when the superconducting transition drops from 8.5 to 1.2 K, the superconducting energy gap  follows perfectly T c . All this is pointing to a two-stage fermionic scenario of the superconductor-insulator transition (SIT) via a metallic state as an alternative to the direct bosonic SIT scenario with a Cooper-pair insulating state evidenced by the last decade STM experiments. [7][8][9][10][11][12][13] bring evidences that upon increasing disorder decreases more slowly than T c , the variation of on a scale of the superconducting coherence length  increases, a pseudogap appears above T c in the tunneling spectra, the spectral coherence peaks are suppressed, and the vortex lattice is fading out. This phenomenology strongly supports the bosonic scenario and raises the question about the universality of the bosonic SIT [14]. On the other hand, potential evidence for the fermionic mechanism was provided even sooner by the tunneling experiments on planar junctions on amorphous Bi and PbBi/Ge films [15,16] indicating that the Cooper pair amplitude vanishes at SIT. But the unambiguousness of these results was challenged by the fact that the spatially averaged tunneling spectra were gapless. This gaplessness could be explained by a very inhomogeneous gap distribution due to phase fluctuations. Then, superconducting pair correlations might also exist in insulators close to SIT, contradicting the fermionic scenario. KeywordsHere, we present sub-Kelvin STM experiments on ultra thin superconducting MoC films with atomic spatial resolution. We demonstrate the spatial homogeneity of the superconducting state for film thicknesses down to 3 nm and the closing of the superconducting energy gap/order parameter as T c vanishes, in agreement with the fermionic scenario. Thus, we bring the first direct evidence on the local behavior of the superconducting order parameter in this class of the transition.The MoC films were prepared by the magnetron reactive sputtering from a Mo target in an argon-acetylene atmosphere onto a sapphire c-cut substrate. The details can be found elsewhere [17]. The preparation followed the procedure of Lee and Ketterson [18] who manufactured continuous MoC films down to 0.4 nm thickness showing

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confidence: 89%

Fermionic scenario for the destruction of superconductivity in ultrathin MoC films evidenced by STM measurements

et al. 2016

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“…Other methods have been used to extend the Mattis-Bardeen equations to incorporate gap broadening and may be more or less applicable to hafnium depending on the exact broadening mechanism. [33][34][35] Thermal distribution functions are also assumed which do not capture potential non-equilibrium effects. 36 As such, the fit should be interpreted to show a qualitative agreement with this model.…”

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confidence: 99%

Design and performance of hafnium optical and near-IR kinetic inductance detectors

Zobrist

Coiffard

Bumble

et al. 2019

Applied Physics Letters

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We report on the design and performance of Microwave Kinetic Inductance Detectors (MKIDs) sensitive to single photons in the optical to near-infrared range using hafnium as the sensor material. Our test device had a superconducting transition temperature of 395 mK and a room temperature normal state resistivity of 97 µΩ cm with an RRR = 1.6. Resonators on the device displayed internal quality factors of around 200 000. Similar to the analysis of MKIDs made from other highly resistive superconductors, we find that modeling the temperature response of the detector requires an extra broadening parameter in the superconducting density of states. Finally, we show that this material and design is compatible with a full-array fabrication process which resulted in pixels with decay times of about 40 µs and resolving powers of ∼9 at 800 nm.Optical and near-IR (OIR) MKIDs are superconducting sensors capable of measuring the arrival time and energy of optical to near-infrared photons. 1 They are less sensitive to false counts and radiation damage 2 than semiconductor devices operating in the same wavelength range and can achieve higher readout speeds. Moreover, each MKID is a high quality factor resonator which allows for natural frequency domain multiplexing and distinguishes the technology from other superconducting detectors. These advantages make arrays of OIR MKIDs useful as astrophysics cameras focusing on timedomain astronomy 3-5 and high contrast imaging. 6-8 To date, commissioned instruments have used either nonstoichiometric titanium nitride or platinum silicide alloys as the photon-sensitive material in the resonators and have achieved resolving powers, R = E/∆E, of up to 8 at 800 nm. 9 This resolving power has been shown to be limited equally by stationary noise, generated by two-level systems (TLS) in the device and amplifiers in the readout chain, as well as an intrinsic variance in the photon signal pulse height, likely caused by phonon escape from the superconductor to the substrate during the initial photon energy down-conversion. 10

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“…27. As a result of disorder, the temperature and frequency dependent complex conductivity σ = σ 1 − iσ 2 deviates from the well known Mattis-Bardeen conductivity, 1,28,29 in contrast to clean BCS superconductors. These deviations were directly related to the complex conductivity of disordered superconductors 1 utilizing Nam's theory.…”

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confidence: 85%

Kinetic planar resonators from strongly disordered ultra-thin MoC superconducting films investigated by transmission line spectroscopy

Baránek,

Neilinger,

Manca

et al. 2021

Preprint

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The non-contact broadband transmission line flip-chip spectroscopy technique is utilized to probe resonances of mmsized square kinetic planar resonators made from strongly disordered molybdenum carbide films, in the GHz frequency range. The temperature dependence of the resonances was analyzed by the complex conductivity of disordered superconductor, as proposed in Ref. 1, which involves the Dynes superconducting density of states. The obtained Dynes broadening parameters relate reasonably to the ones estimated from scanning tunneling spectroscopy measurements. The eigenmodes of the kinetic planar 2D resonator were visualized by EM model in Sonnet software. The proper understanding of the nature of these resonances can help to eliminate them, or utilize them e.g. as filters.

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Finite quasiparticle lifetime in disordered superconductors

Cited by 26 publications

References 29 publications

Fermionic scenario for the destruction of superconductivity in ultrathin MoC films evidenced by STM measurements

Fermionic scenario for the destruction of superconductivity in ultrathin MoC films evidenced by STM measurements

Design and performance of hafnium optical and near-IR kinetic inductance detectors

Kinetic planar resonators from strongly disordered ultra-thin MoC superconducting films investigated by transmission line spectroscopy

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